As solid human cancer tumors form there are a number of physiological changes that occur within the tumor itself. These changes include low oxygen levels (hypoxia) and an accumulation of lactic acid with concomitant lowered pH levels (lactic acidosis). In order to adapt to and survive in these physiological stresses, human cancer cells in solid tumors exhibit significant genetic and metabolic changes. While transcriptional responses and downstream signaling events are known in certain contexts of these stresses, a systematic genome-wide investigation of which genes are critical for cell survival in these TME stresses has not been examined. The central hypothesis of my proposal is that understanding the function of genes that modulate cell survival under TME stresses will allow for the development of treatments to specifically target cancer cells under TME stress conditions. To investigate this hypothesis, I propose applying the concept of synthetic lethality to cultured cancer cells by combining individual gene expression knockdown with the application of hypoxia or lactic acidosis. Our lab recently identified synthetically lethal genes for breast cancer cell survival under one TME stress, and so we expect that applying the concept genome-wide is likely to reveal other novel critical regulators. Aim 1 will identify the genes that improve or reduce cellular fitness under two TME stresses on a genome-wide scale by two different screen approaches. Aim 2 will investigate the mechanisms of specific gene candidates validated as hits from Aim 1. The goal of this project is to better understand how cancer cells adapt to and survive in the TME stresses. This knowledge will allow for a better understanding of the genetic changes selected by the TME and improve therapies to target solid human cancers in the future.